Phase balancing apparatus



March 27, 1951 s. B. CRARY 2,546,725

PHASE BALANCING APPARATUS Filed 001:. 29, 1949 T F 8 H '9 f L 5 L JInven tor Selderfi B Crary, by

His Attorney.

Patented Mar. 27, 1951 2,546,725 PHASE BALANCING APPARATUS Selden B.Crary, Schenectady, N. Y., assignor to General Electric Company, acorporation of New York Application October 29, 1949, Serial N 0.124,410

4 Claims.

This invention relates to electrical supply systems and moreparticularly to a static impedance and individually variable taptransformer phase balancing apparatus for use in polyphase supplysystems.

The general principles f balancing phase voltages and currenLs inpolyphase supply systems by the use of capacitive and inductivreactances are well known. In the case of unbalanced loading on apolyphase system, as for example due to a substantial single-phase load,such reactances may be connected across the various phases of the supplyto provide components of current which combine with otherwiseunsymmetrical currents produced b unbalanced loading, to providesubstantially symmetrical currents in the phase lines. Thus by the useof single-phase impedances connected across individual phases it ispossible to correct the voltages along the line of an unbalanced supplysystem and at the same time to effect a balancing of the currents andloads between phases.

A particular advantage of such balancing is the reduction innegative-phase sequence currents which may be required to flow in apolyphase transmission system and more particularly in rotatinggenerating apparatus associated ther with due to unbalanced loading ofthe systemj By reducing negative-phase sequence current to a minimum asubstantial reduction in amortisseur winding heating in the rotatingmachine may be effected.

It is the principal object of my invention to provide a new and improvedindividually variable tap transformer apparatus for balancing thecurrents and voltages in polyphase transmission systemsby the use ofstatic impedance elements.

In accordance with a preferred embodiment of my invention, I provide anumber of single-phase transformers each connected across a phase of apolyphase transmission system and each arranged to impress a voltage,adjustable through a tapchanging arrangement, on a' suitable reactance;By adjusting, either manually or automatically, the tap voltagesimpressed on the individual reactances, reactive currents areprovidedwhich combine with load currents to' effect balanced conditions ofcurrent and voltage between the phases of the transmission system.

The invention will be better understood from a consideration of thefollowing description taken in connection with the accompanying drawingand the appended claims, in which the featuresv of the invention.believed to be novel are more particularly set forth;

Referring now to the single figure of the drawing, there is shown apolyphase supply system comprising a transmission system I connectedto'A single-phase load impedance 1 representedas including a resistance 8and an inductive reactance 9 is shown connected to phases A and B oftransmission system I. It i assumed that load impedance I is located ata considerable distance from generator 2 and that accordinglytransmission system I is relatively great in length. Load I, due to thepower limitations of generator 2 and the relatively great length oftransmission system I, causes a considerable unbalance in the voltagesof lines 3, 4 and 5. Such unbalanced loading likewise causes anunbalance of the currents in phases A, B and C and in the windings ofgenerator 2.

In accordance with my invention I provide substantiall identicalcompensating devices III, II and I2 connected across phase voltages BC,CA, and AB respectively of transmission system I at the vicinity ofsingle-phase load I or at the point where balancing action is desired,to compensate for the unbalance created by load I. Since devices III, IIand I2 are substantially identical, it will be understood that thefollowing description of device I II is intended to serve also as adescription of devices II and I2. l Device ID comprises a transformer I3having a magnetic core I4, a primary winding I5, a main secondarywinding I6, and an auxiliary secondary winding I'I. Winding I5 isconnected to lines land 5 of system I or across phase voltage BCthereof. Main secondary winding I6 is provided with a pair of outputterminals I8 and I9. Ter-' minal I8 may conveniently be one extremity ofwinding I6. Terminal I9 is arranged to tap winding IE5 at various pointsthereof by the use of a suitable tap-switching mechanism 29 comprising.a switch arm 2| and a plurality of taps 22 connected to the otherextremity 23 of winding I6 and various intermediate points betweenextremities I8 and 23. A reactance element represented as a capacitivereactance 24 is connected between output terminals I8 and I9 of windingI5. As switch arm 2 I is caused to make contact with th varioustaps 22of winding I6 the voltage impressed on capacitive reactance 24 is causedto be varied,

Tap-switching mechanism is operated by a reversible motor supplied withpower from auxiliary secondar winding I1. Motor 25 is provided with asplit-series field 26 having opposite portions 21 and 28 joined at acommon point 29 which is connected to one extremity 30 of winding I1.

The free ends oi; field. members; 2;] 1 ands 28931 connected to contacts3| and 32 of a contactmaking voltmeter 33. voltmeter 33 has a poten;.tial coil 34 connected across winding l1, and a movable pointer 35responsive tothe-magnetioforces of potential coil 34. Pointer 35servesas a movable contact which is, connected. to entremity 36 ofwinding H. Pointer 35 is arranged to engage either contact 3| or contact3 2 to com plete the circuit from winding l=1-through-eitherfield member21 or 28, respectively, to causerfprr. ward or reverse rotatiomof motor25. v

It.- i; be. understood that. transiormors. 13 formin me s-oi: c mp natin .devic s. i oshoroino io may.beautomati tapvoiiana ns e u tiansformers. o a. well. n wn. ooli i ion l p s hamannor ihi9lT l ..l1 atapschanging transjormer, is construc ted .is not ar of my, inv nt nnd-accordin ious. auxilia y d vices. conve t onal y us d. n; auto: m t-sh m n r nsf rmers, such. as imi switches or otor. -.5 nd.an-adipsti smoh nismi or. ntact-maki g oltmet r 3'. re ot s own in e. draw nei.

n a tin to. b, lance e. oadsndolta s nitr nsm ssion. yst m ompen a ng,de es 11.112. ot. as: ulat n evic s es onsi o. he. v a es. imp e s dupon, the p imary W nd: nss I her f n-narti. u or, ons de n now. heon rt on i... vic, D. ,the volta e im res ed. nboil 3. .01 ontra t maisinaol moter. 3'is. r

o hei rnsoi. winding. I 5. to nhases ltaae 1B9 ontaoismais ne oimoton-"ii is adiiisted y. a,

Ao ord n lv, o ooih 4-. difio s rom. he; set ltage. po n e s. on cos. nac 31. or. .2..torausaexoitation i. ioldiwindin 2B:.. nd...rotation- I-:mo or. 5'." Wh n hase volta iq siowo haiithoayoraeo al a ei o mo or. .5.s. rr n ed. tate. 1 oiiisrm lt na i oo nto inorease hov ltesa mpr s sdnoapao ti o. eaotance2: thereby increasing the reactive currentvtherein; Thus nflnomaso snrovidod nthsxoaohve curren omp n nt n inesvand. Similar d vices. '1. and. 2 ause. hanges o... e. Provided: he osotve 1 com onents in. ines... n .,ondfl inos 3-;and. i. resnective1v,thr uh hei o la i el ac: ion of ra s rmers. I 3... and h aa hansina me h nsms. s oiatodi h rowith.

n e er l am han in mechanisms- 9'; of. ioy es M1,, and I2do nohhave idenoaLset: ings, 1 1 toady tato. ndition of ystem.- 11 other words s.hown-i fihadr win w ch. arm.. 2.! m y be. diust di to the, cent r ap owindin Iii-oi; device it. while, arm 2,! i. ev ce U. m hoa di stedmtdasan below he center tap, and to a tap above the cententantin the aseoi, dvi e... 2 Thonositiorr of; rm .1 for aim t u ar. do ool uch. e e. s.. 1v. d rm no he.-.resn atins;. otioni l ontaot maki s ltm ter and motor..5.; s oo od herewit n .ao o g noe with. v..oil.., now mm: oipios... t.will. e unde stood ov es n;

H and I2 act independently and in each case an when the. volta e. mnresos i on,

attempt is made to cause the phase voltage impressed on a particularcompensating device to be brought to the average value of phase voltageto which the contact-making voltmeter is adjusted.

A voltage correction taking place in system I action of devices It, ILand, l 2,r.es 1lts from theoombinatiomof thereactive components ofcurrent provided by devices H], H and I2 and the load currents providedby load I. It is well known that if a balance is effected in the phasecur-rents in a system such as system I, then a halance o frthephasevoltages is likewise obtained. Eurthermore; icy-balancing thecurrents in system I, a reduction, is-vobtained in the negative-phasesequence currents flowing therein and in genera-tori; thereby-reducingthe amortisseur winding. heating in generator 2. Thus by the use ofcompensating devices in accordance with my invention a regulating actionis obtained along ha inos. of. an. u b lan d, transmission. sy em o ethr. with ahal noin f u r -n s; d oads between phases, and a reduction of"negativephase sequence currents.

While I. have shown in the embodiment here?- ir describeda number ofsingle-phase tap -chang ir g transformers of? conventional type in" com:bination with capacitive reactances; it wil1= be? understood that myinvention is not: limited to; the use of 1 single-phase transformersorcapacitivereactances. Under certain flco nditions"it maye be desirableto make use of 'induct-ive"reactances; or acombination ofcapacitiveorinductive-react ances in the variousgphases; Furthermore;it. maybe desirable to employ other typesand; ar rangemerits ofadjustable; voltage; transformers; such as polyphase transformershavingindividual' tap-changing mechanisms forthe various-phases;

While I; have shown and described" a preferred?- embodiment of myinvention, it willbe under:- stood that my invention may well'takeother: forms, and I, therefore, aim inthe appendedclaims to coverall such-changes and:modifica; tions as fall'within the true spirit'andscope of L the invention.

What I; claim as new and desire to secure by; Iigetters Patent of theUnited- States is:-

l'-.- Ina' polyphase electricaltransmission system havingan'unbalancedload connected-thereto, transformer means associatedwiththe phases of saidsystem and* having" an adjustable tapvoltagecorresponding to each of said phases,; a reactive element associatedwith each of; said phases and connected to the transformer tap; voltage,corresppnding thereto;v and'means to adjust said tap volta es.individually to, provide; eact ve. urren s s aiciisv tom o. end o. aslice. he. ghost: lta es nd urr n s her n:

2-. na po y hs e olootrioal't an m om .hav ngan unbalancedlloasisonneotedh iio to ransiormenmeans assoc ated-with hem... es. i. said.system. an hav n djus able tan. oi aao orro pon ins, o, ea h of,saidrnhasosa apaciti e r a an element s ocia d; w th; aoho sa dunh sesaridoon e toslf o hoztransr o mer. p, ol a e r espondin h r to, n means.to. ad ust ai L ap olta e div duallh to provide reactive currentsinsaidsystem to omito alanooth has oltages an u ont b.oro

In polvphaso. e ica ra smiss o v tern having an unbalancedjloadconnectedthere o transi mormoons ssooiat jwitii l1R 3?i of'said systemand having an adjustablotap voltage corresponding to each"of-'said"phas'es;

and automatic means to adjust said voltage taps individually to providereactive currents in said system to tend to balance the phase voltagesand currents therein.

SELDEN B. CRARY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,551,270 Slepian Aug. 25, 19 51,658,980 Fortescue Feb. 14, 1928

